1. Field of the Invention
The present invention relates generally to the field of communication receivers, and more particularly to an alerting system which utilizes a rechargeable back-up battery.
2. Description of the Prior Art
Selective call communication receivers, such as pagers, have utilized a variety of alerting devices to provide an alerting function which is intended to alert the user when a message is received. The alerting devices utilized have included such devices as speakers and audio transducers to provide audible alerts, LED's to provide visual alerts, and vibrators to provide tactile alerts. Each of the alerting devices have different energy consumption requirements. LED's, for example, have generally required the least amount of energy, or power, to provide a visual alert. Speakers and audio transducers have generally required a greater amount of energy, the actual amount of energy required being determined by the device impedance and the volume, or sound pressure level (SPL) output required from the speaker or audio transducer. Vibrators, which have generally utilized motors to spin an unbalanced counterweight, have the highest energy requirements, significantly greater than either LED's and speakers or audio transducers.
Previous selective call receivers have often included one or more of the alerting devices to provide different alerts to meet different user needs. For example, audio transducers were regularly offered in selective call receivers with vibrators to provide an audible alert when such an alert was not annoying to others, and a vibrator, or "silent" alert when an alert would be annoying to others, or when privacy was desired.
More recently, advances in components and technology have enabled significant reductions in the size of the selective call receivers. However, as the size of the selective call receivers has diminished due to the improvements in components and technology, it has become significantly more difficult to provide both audible and tactile alerting functions. This is especially true for such selective call receiver design formats as the "wrist watch" and "credit card" pager formats. As the size of the selective call receiver has come down, so too has the size of the battery had to be reduced in order to fit into the smaller receiver design formats. In order to maintain reasonable battery life in such receivers, newer battery technologies have had to be utilized, such as those provided by zinc-air and lithium battery technologies. However, the newer battery technologies, while improving the battery life for selective call receivers using visual or audible alerts, are generally incapable of supplying the necessary power to drive a vibrator, due to the significantly higher internal cell impedances. Consequently, there is a need to provide a way to utilize a vibrator in the small selective call receiver design formats which do not unduly impact the size of the receiver, and which do not compromise the use of the higher energy content zinc-air and lithium battery technologies.